A skydiver jumps from a flying plane. his height from earth is given through formula h=400+3t-4.9t^2. 1. in which moment the velocity is 46m/s?

2. find the momentum acceleration

Now I've solved it but I'm not sure whether I found it correctly or not.
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3. a particle with initial velocity v⃗ 0=(5.85×103m/s)j^ enters a region of uniform electric and magnetic fields. the magnetic field in the region is b⃗ =−(1.35t)k^. you can ignore the weight of the particle. a. calculate the magnitude of the electric field in the region if the particle is to pass through undeflected, for a particle of charge +0.640 nc.